Enhanced lube oil yield by low hydrogen pressure catalytic dewaxing of paraffin wax

ABSTRACT

Catalytic dewaxing of paraffin containing feeds, preferably feeds produced from a non-shifting Fischer-Tropsch catalyst, is accomplished at relatively low hydrogen partial pressures without substantial affect on the life of a catalyst having a certain pore structure.

FIELD OF THE INVENTION

[0001] This invention relates to a process for catalytically dewaxing paraffin containing hydrocarbons. More particularly, this invention relates to the production of lube base oils having a pre-determined or pre-selected pour point by catalytically dewaxing a paraffin containing feed at low hydrogen partial pressures.

BACKGROUND OF THE INVENTION

[0002] The production of lube base oils by hydroprocessing paraffin containing feeds is well known, e.g., hydroisomerization or hydrocracking of the feed to produce lube base oils. These processes are catalytic and are usually carried out at relatively high hydrogen pressures, e.g., >500 psig hydrogen partial pressures. Catalytic dewaxing is a form of hydroprocessing and involves paraffin isomerization and some hydrocracking in the production of lube base oils.

[0003] Hydrogen has always been used in the hydroprocessing, i.e., isomerization, cracking, dewaxing, of paraffins to produce lube base oils. Hydrogen is believed to be important for promoting extended catalyst life by e.g., reductive coke removal; see, for example U.S. Pat. No. 4,872,968. The hydrogen partial pressures usually employed in catalytic dewaxing processes range from about 200 psig to about 1000 psig or more, e.g., see U.S. Pat. No. 5,614,079 with hydrogen pressures in the higher end of this range being preferred—for reasons of catalyst life.

[0004] U.S. Pat. No. 5,362,378 discloses hydrogen partial pressures of 72-2305 psig for use with large pore zeolite beta. This patent does not mention catalyst life or TIR, i.e., temperature increase required, necessary for maintaining product specifications, such as pour point or cloud point.

[0005] We have now found, however, that a particular combination of features allows for conducting catalytic dewaxing at low hydrogen pressures and conditions that are selective to hydroisomerization with little or no hydrocracking, without sacrificing catalyst life.

SUMMARY OF THE INVENTION

[0006] In an embodiment of this invention, a paraffin containing feed, preferably a feed containing at least 80 wt % paraffins, can be catalytically dewaxed in the presence of a molecular sieve catalyst with one dimensional pore structures having an average diameter of 0.50 nm to 0.65 nm, wherein the difference between the maximum diameter and the minimum diameter is preferably ≦0.05 nm. The molecular sieve catalyst is exemplified by, for example, ZSM-23, ZSM-35, ZSM-48, ZSM-22, SSZ-32, zeolite beta, mordenite and rare earth ion exchanged ferrierite in conjunction with a dehydrogenation component. Preferably, the molecular sieve catalyst is ZSM-48 (ZSM-48 zeolites herein include EU-2, EU-11 and ZBM-30 which are structurally equivalent to ZSM-48) with a dehydrogenation component. The dewaxing process is carried out at hydrogen partial pressures of less than about 500 psig while maintaining a catalyst deactivation rate of less than 30° F./year.

[0007] The invention includes a catalytic dewaxing process comprising contacting an 80+% paraffin containing feed at dewaxing conditions including a hydrogen partial pressure of less than about 500 psig with a catalyst comprised of a molecular sieve with a one dimensional pore structure having an average diameter of 0.50 to 0.65 nm and a metal dehydrogenation component, the catalyst having a deactivation rate, measured by temperature increase required (TIR) for meeting a pre-determined pour point or cloud point, of less than 30° F./year.

[0008] Catalyst deactivation rate is reported herein as TIR; that is “temperature increase required” for maintaining a pre-determined pour point, the predetermined pour point preferably being less than about −12° C., more preferably less than about −21° C. Catalytic dewaxing is, essentially, the conversion of n-paraffins to branched paraffins. That is, the conversion of waxy molecules to molecules exhibiting better flow properties, particularly at lower temperatures.

DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a plot of pour point, ° C. (ordinate) against temperature, ° F. (abscissa) showing that catalytic activity increases with decreasing hydrogen pressure.

[0010]FIG. 2 is a plot of % conversion (ordinate) against pour point, ° C. (abscissa) showing that selectivity to isomerization increases with decreasing hydrogen pressure.

[0011]FIG. 3 is a plot of average reactor temperature, ° F. (ordinate) against days on stream (abscissa) and shows a deactivation rate by regression when producing a lube base oil of −21° C. pour point at a hydrogen partial pressure of 150 psig.

[0012]FIG. 4 is a plot of Temperature, ° C. (ordinate) against days on stream (abscissa) at 250 psig hydrogen pressure to meet a diesel cloud point of −15° C.

[0013]FIG. 5 is a plot similar to FIG. 4 to meet a −21° C. wide cut lube base oil pour point.

[0014]FIG. 6 is a plot of reactor temperature, ° F. (ordinate) against days on stream (abscissa) to meet a −21° C. pour point for a 700-950° F. isomerate.

[0015]FIG. 7 is a plot of reactor temperature, ° F. (ordinate) against days on stream (abscissa) to meet a +8° C. cloud point for a 950° F.+ isomerate.

[0016] For the particular set of features described herein, reducing hydrogen partial pressure results in increased catalyst activity, and increased yield. That is, the increase in activity is almost entirely an increase isomerization activity, and little hydrocracking occurs. Nevertheless, while decreasing hydrogen partial pressure should result in decreased catalyst life, the features of this invention show that catalyst life is not sacrificed.

[0017] For purposes of this invention, pour point is determined by ASTM D-5950, cloud point is determined by ASTM D-5773.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The feed that can be employed in various embodiments of this invention is a paraffin containing feed, preferably a feed that contains greater than 80 wt % n-paraffins, more preferably greater than 90 wt % n-paraffins, still more preferably greater than 95 wt % n-paraffins and still more preferably 98 wt % n-paraffins. The feed generally boils in the range 430° F.+, preferably 450° F.+, more preferably 450-1200° F. (minor amounts, e.g., less than about 10% of 1200° F.+ material may be present).

[0019] The feed is preferably low in unsaturates, that is, low in both aromatics and olefins. Preferably, the unsaturates level is less than 10 wt %, preferably less than 5 wt %, more preferably less than 2 wt %. Also, the feed is relatively low in nitrogen and sulfur, e.g., less than 50 wppm of each. Where a Fischer-Tropsch derived feed is employed, there is no need to pre-sulfide the catalyst, and indeed, pre-sulfiding should be avoided.

[0020] Most preferably, the feed is the product of a Fischer-Tropsch reaction that produces essentially n-paraffins, and still more preferably the Fischer-Tropsch process is conducted with a non-shifting catalyst, e.g., cobalt or ruthenium, preferably a cobalt containing catalyst.

[0021] The catalyst employed in the catalytic dewaxing step comprises a molecular sieve with one dimensional pore structure and a metal dehydrogenation component. The molecular sieves include ZSM-23, ZSM-35, ZSM-22, SSZ-32, zeolite beta, mordenite and rare earth ion exchanged ferrierite. Preferably, a ZSM-48 catalyst containing a metal dehydrogenation functionality, preferably supplied by the presence of platinum or palladium or both platinum and palladium, preferably platinum.

[0022] The molecular sieve catalyst support is described in J. Schlenker, et al., Zeolites 1985, vol. 5, November, 355-358, hereby incorporated by reference. ZSM-48 is characterized by the X-ray diffraction pattern shown in Table 1 below. The material is further characterized by the fact that it exhibits a single line within the range of 11.8±0.2 Angstrom units. The presence of a single line at the indicated spacing structurally distinguishes ZSM-48 from closely related materials such as ZSM-12 (described in U.S. Pat. No. 3,832,449) which has two lines, i.e., a doublet, at 11.8±0.2 Angstrom units, and high silica ZSM-12 (described in U.S. Pat. No. 4,104,294) which also has a doublet at the indicated spacing. TABLE 1 Characteristic lines of ZSM-48 (calcined, Na Exchanged Form) d(A) Relative Intensity (I/I_(O)) 11.8 ± 0.2 S 10.2 ± 0.2 W-M  7.2 ± 0.15 W  4.2 ± 0.08 VS  3.9 ± 0.08 VS  3.6 ± 0.06 W  3.1 ± 0.05 W  2.85 ± 0.05 W

[0023] The values were determined by standard technique, i.e., radiation was K-alpha doublet of copper, and diffractometer equipped with a scintillation counter. The peak heights, I, and the positions as a function of two times theta, where theta is the Bragg angle, were determined by a compactor. From these the relative intensities, 100 I/I_(O), where I_(O) is the intensity of the strongest line or peak, and d(obs.), the interplanar spacing in A corresponding to the recorded lines, were calculated. Table 1 gives the intensities in terms of the symbols W=weak, VS=very strong, M=medium, and W−S=weak to strong (depending on the cationic form). Ion exchange of the sodium ion with other cations reveals substantially the same pattern with some minor shifts in interplanar spacing and variation in relative intensity. Other minor variations can occur depending on the silicon to aluminum ratio of the particular sample, as well as any subsequent thermal treatment.

[0024] ZSM-48 and methods for its preparation are described in U.S. Pat. Nos. 4,375,573; 4,397,827; 4,448,675; 4,423,021; and 5,075,269. The method of preparation described in U.S. Pat. No. 5,075,269 is particularly preferred, and is incorporated herein by reference. This method is for preparing a catalyst particularly suitable for the catalytic dewaxing process.

[0025] The zeolite, ZSM-48, and other utilizable zeolites such as ZSM-23, ZSM-35, ZSM-22, SSZ-32, zeolite beta, mordenite and rare earth ion exchanged ferrierite are usually employed with a dehydrogenation component in an amount of about 0.01 to 5.0 wt/o, the component being manganese, tungsten, vanadium, zinc, chromium, molybdenum, rhenium, Group VIII metals such as nickel, cobalt, or the noble metals platinum and palladium. The noble metals are preferred components. Such component can be exchanged into the composition, impregnated thereon, or physically intimately admixed therewith. Such component can be impregnated in or onto the zeolite such as, for example, in the case of platinum, by treating the zeolite with a platinum metal-containing ion. Thus, suitable platinum compounds include chloroplatinic acid, platinous chloride and various compounds containing the platinum tetra-ammonia complex. Platinum and palladium are preferred hydrogenation components.

[0026] The compounds of the useful platinum or other metals can be divided into compounds in which the metal is present in the cation of the compound and compounds in which it is present in the anion of the compound. Both types of compounds which contain the metal in the ionic state can be used. A solution in which platinum metals are in the form of a cation or cationic complex, e.g., Pt(NH₃)₄Cl₂, is particularly useful.

[0027] Prior to its use, the ZSM-48 catalyst should be dehydrated at least partially. This can be done by heating to a temperature in the range of from about 100° C. to about 600° C. in an inert atmosphere, such as air, nitrogen, etc., and at atmospheric or subatmospheric pressures for between 1 and 48 hours. Dehydration can also be performed at lower temperature merely by placing the catalyst in a vacuum, but a longer time is required to obtain sufficient amount of dehydration. ZSM-48 is formed in a wide variety of particle sizes. Generally speaking, the particles can be in the form of a powder, a granule, or a molded product, such as extrudate having a particle size sufficient to pass through a 2 mesh (Tyler) screen and be retained on a 400 mesh (Tyler) screen. In cases where the catalyst is molded, such as by extrusion, the crystalline silicate can be extruded before drying or dried or partially dried and then extruded.

[0028] As in the case of many other zeolite catalysts, it may be desired to incorporate the ZSM-48 with a matrix material which is resistant to the temperatures and other conditions employed in the dewaxing process herein. Such matrix materials include active and inactive materials and synthetic or naturally occurring zeolites as well as inorganic materials such as clays, silica and/or metal oxides e.g., alumina. The latter may be either naturally occurring or in the form of gelatinous precipitates, sols or gels including mixtures of silica and metal oxides. Use of a material in conjunction with the ZSM-48, i.e., combined therewith, which is active, may enhance the conversion and/or selectivity of the catalyst herein. Inactive materials suitably serve as diluents to control the amount of conversion in a given process so that products can be obtained economically and orderly without employing other means for controlling the rate or reaction. Frequently, crystalline silicate materials have been incorporated into naturally occurring clays, e.g., bentonite and kaolin. These materials, i.e., clays, oxides, etc., function, in part, as binders for the catalyst. It is desirable to provide a catalyst having good crush strength since in a petroleum refinery the catalyst is often subject to rough handling which tends to break the catalyst down into powder-like materials which cause problems in processing.

[0029] Naturally occurring clays which can be composited with ZSM-48 include the montmorillonite and kaolin families which include the sub-bentonites, and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays, or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite or anauxite. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification.

[0030] In addition to the foregoing materials, ZSM-48 can be composited with a porous matrix material such as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, as well as ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia. The matrix can be in the form of a cogel. Mixtures of these components can also be used. The relative proportions of finely divided crystalline silicate ZSM-48 and inorganic oxide gel matrix vary widely with the crystalline silicate content ranging from about 1 to about 90 percent by weight, and more usually in the range of about 2 to about 80 percent by weight, of the composite.

[0031] In general, reaction conditions for dewaxing may vary widely even when the hydrogen partial pressures are maintained at low levels. Thus, start of run temperatures may vary between about 550-650° F. (288-343° C.). End of run conditions can be defined by the nature of the product being produced, for example, when predetermined color specifications can no longer be met (an indication of catalyst deactivation), or when the predetermined pour point or cloud point can no longer be obtained, or the selectivity to isomerization is reduced as evidenced by an increase in methane yield due to hydrocracking. In general, however, end of run temperatures should be less than about 800° F. (427° C.), preferably less than about 750° F. (399° C.), more preferably less than about 725° F. (385° C.).

[0032] In one embodiment of this invention, hydrogen partial pressure is maintained as low as reasonably possible without sacrificing desired catalyst life. Catalyst life may be longer or shorter depending on desired results and severity of the dewaxing process, i.e., higher severity obtained by increasing temperature or decreasing feed velocity, or both. However, at end of run conditions the catalyst must be either rejuvenated or replaced, if rejuvenation is no longer possible. In either case the unit must be shut down and valuable operating time is lost. Reasonable catalyst life will be a function of operator choice but, measured by TIR, is preferably not more than 30° F./year, more preferably less than 25° F./year, still more preferably less than 20° F./year, and still more preferably less than 10° F./year. In another aspect of this invention, the catalyst deactivation rate at dewaxing conditions allows the process to be carried out, while still meeting a predetermined pour point or cloud point, for a period of at least six months, preferably at least about twelve months, more preferably at least about 18 months, and still more preferably for at least about 24 months, or longer, for example, greater than 30 months or greater than 36 months.

[0033] Catalyst deactivation is believed to be a result of coke formation on the surface of the catalyst, the coke covering or blocking access to the catalytic metal, as well as blocking the pores of the zeolite.

[0034] The catalyst may be regenerated by known methods including hot hydrogen stripping, coke removal by oxygen treatment or a combination of hydrogen stripping and oxygen treatment.

[0035] Briefly, hydrogen stripping can be carried out with hydrogen or a mixture of hydrogen and an inert gas such as nitrogen, at isomerization reaction temperatures for a period of time sufficient to allow the catalyst to regain at least about 80%, preferably at least about 90% of its original lined out activity. Oxygen treatment can be carried out at calcining conditions, e.g., using air at temperatures from about 500° C. to 650° C., again for a period of time sufficient to allow the catalyst to regain at least about 80%, preferably at least about 90% of initial lined out activity after subsequent reduction.

[0036] The catalyst life requirements can be satisfied with positive hydrogen partial pressures greater than 0 psig and less than 400 psig, preferably at hydrogen partial pressures ranging from about 100-400 psig, more preferably about 100-350 psig, and still more preferably at about 150-350 psig.

[0037] The catalyst may be sulfided or unsulfided. Where low sulfur feeds are used, e.g., derived from the Fischer-Tropsch process, the catalyst is preferably unsulfided. In general, other gases may be present and will not interfere with the reaction. Such other gases may be nitrogen, methane, or other light hydrocarbons (that may be produced during the reaction). Total pressure may range up to 2000 psi, preferably 100-2000 psi, more preferably 150-1000 psi, still more preferably 150-500 psi. Hydrogen can make up 50-100% of total gas, preferably 70-100%, more preferably 70-90%. At the low hydrogen partial pressures recited herein small amounts of olefins and aromatics may be produced, and hydrofinishing, at well known conditions, may be necessary to remove these components.

[0038] The liquid hourly space velocity is generally between about 0.1 and about 10, and preferably is generally between about 0.5 and 4. The hydrogen to feed ratio is generally between about 100 and about 10,000, and preferably between about 800 and about 4,000 standard cubic feet (scf) of hydrogen per barrel of fuel.

[0039] Alpha Value is an approximate indication of the catalytic cracking activity of the catalyst compared to a standard catalyst and provides a relative rate constant (rate of normal hexane conversion per volume of catalyst per unit time). The value is based on the activity of a silica-alumina cracking catalyst taken as an Alpha of 1 (rate constant=0.016 sec⁻¹). The test for Alpha Value is described in U.S. Pat. No. 3,354,078 in the Journal of Catalysis. vol. 4, p. 527 (1965); vol. 6, p. 278 (1966); and vol. 61. 395 (1980), each incorporated herein by reference. The Alpha Value of the catalyst prior to metal loading is preferably in the range of about 10 to about 50.

[0040] The following examples will serve to illustrate this invention:

EXAMPLE 1

[0041] This example explores the benefits in lube base oil yield obtained as hydrogen partial pressure is reduced from 500 to 150 psig. The following unit conditions and process variables were studied with ZSM-48 using a wide cut Fischer-Tropsch feed, i.e., 430° F.+ feed.

[0042] Catalytic dewaxing was carried out in a downflow reactor simulating a trickle bed reactor immersed in a sand bath to maintain isothermal reactor conditions. The reactor contained 80 cc of an unsulfided ZSM-48 catalyst with 0.6 wt % Pt diluted with glass beads. Conversion of a 430° F.+ wax obtained from a cobalt slurry catalyzed Fischer-Tropsch process was controlled by temperature.

[0043] The process was operated at temperatures ranging from 580-640° F. with reactor hydrogen pressures, at the reactor exit of 150-500 psig. The hydrogen treat gas rate was 1800-2500 scf/bbl, and the liquid hourly space velocity was 1.25 v/v/hr.

[0044] The liquid product was fractionated by 15/5 distillation unit and the following fractions were recovered: IBP/320° F., 320/700° F., and 700° F.+. The 700° F.+ fraction was analyzed for pour and cloud points, and kinematic viscosity and viscosity index; the 320/700° F. fraction was analyzed for cloud point.

[0045] In FIG. 1, lines A, B, and C refer to hydrogen pressures of 150, 250, and 500 psig. At a pour point of −21° C., catalytic activity increases with decreasing operating pressure, as shown in Table 2 below. TABLE 2 Operating H₂ Pressure, psig Temperature required for −21° C. P.P. 500 627.4 250 612.8 150 602.8

[0046] Because the kinetics of the dewaxing process are negative second order in hydrogen the activity increase with reduced pressure may be anticipated.

[0047] Selectivity to lubes increased with decreasing hydrogen pressure. In FIG. 2, where lines A, B, and C again refer to hydrogen pressures of 150, 250, and 500 psig. The lubes yield, (i.e., 1-conversion), at a −21° C. pour point is shown for each pressure in Table 3, below. TABLE 3 Operating H₂ Pressure, psig Lubes Yield, at −21° C. P.P., % 500 66.7 250 73.9 150 77.7

[0048] The data show that catalyst activity and lube selectivity increased at lower pressure. Consequently, overall lube yield increased.

[0049] Nevertheless, the prevailing wisdom is that catalyst life decreases substantially as hydrogen pressure decreases, thereby leading to shortened on stream periods and longer down times. To determine the effect of reduced hydrogen pressure on catalyst life (and the rate of catalyst deactivation) another experiment was conducted over a period of 70 days at 150 psig hydrogen pressure and producing lube base oil of −21° C. pour point. By regression, the deactivation rate was 21° F./year, by two point activity check the deactivation rate was 26° F./year. Consequently, operating at a very low hydrogen pressure results in a quite acceptable deactivation rate, and clearly suggests that hydrogen pressures of less than 150 psig, e.g., 125 psig, or less than 100 psig, e.g., about 75 psig, will benefit both selectivity to isomerization and increased lube base oil yield while maintaining deactivation rates of less than about 30° F./year, or preferably less than about 25° F./year, and more preferably less than about 15° F./year.

EXAMPLE 2

[0050] The reactor described in Example 1 was operated with a 430° F.+ wide cut Fischer-Tropsch wax feed to study the operation of a dewaxing unit at 250 psig. The catalyst of Example 1 was used, as well. The hydrogen treat gas rate was 2500 SCF/bbl. The liquid hourly space velocity was 1.0. Temperature was adjusted to meet lube pour point or diesel cloud point. When operated to meet a diesel cloud point of −15° C., the deactivation rate was less than 1.8° F./year (1° C./year). The results are shown in FIG. 4.

[0051] Operation of this unit to meet a −21° C. wide-cut lube pour point resulted in a deactivation rate of about 3° C./year (5.4° F./year). The results are shown in FIG. 5.

EXAMPLE 3

[0052] The same feed as used in Example 1 was hydroisomerized and the isomerate was distilled into two fractions: (i) 700-950° F. light cut, and (ii) a 950° F.+ heavy cut. Each fraction was processed in the reactor described in Example 1 and conditions described in Example 2 to meet a −21° C. pour point and a cloud point of +8° C., respectively. Each fraction was run for four (4) months. The results are shown in FIGS. 6 and 7; FIG. 6 showing a deactivation rate (by regression) for fraction (i) of about 2° F./year, FIG. 7 showing a deactivation rate (by regression) for fraction (ii) of about 2° F./year. 

What is claimed is:
 1. A catalytic dewaxing process comprising contacting an 80+% paraffin containing feed at dewaxing conditions including a hydrogen partial pressure of less than about 500 psig with a catalyst comprised of a molecular sieve with a one dimensional pore structure having an average diameter of 0.50 to 0.65 nm and a metal dehydrogenation component, the catalyst having a deactivation rate, measured by temperature increase required (TIR) for meeting a pre-determined pour point or cloud point, of less than 30° F./year.
 2. The process of claim 1 wherein the hydrogen partial pressure is less than 400 psig.
 3. The process of claim 2 wherein TIR is less than 25° F./year.
 4. The process of claim 3 wherein the paraffin containing feed contains greater than 80 wt % paraffins and boils in the range above 430° F.
 5. The process of claim 4 wherein the feed is derived from a Fischer-Tropsch process and contains less than 50 wppm each of nitrogen and sulfur.
 6. The process of claim 5 wherein the dehydrogenation component is platinum or palladium.
 7. The process of claim 6 wherein the hydrogen partial pressure ranges from about 100 to about 350 psig.
 8. The process of claim 7 wherein reaction temperatures ranges from about 550° F. to about 800° F.
 9. The process of claim 7 wherein total reaction pressure ranges from about 100 to about 2000 psi.
 10. The process of claim 7 wherein the pour point is −21° C. or lower.
 11. The process of claim 7 wherein the product of the catalytic dewaxing process is a lube base stock or a diesel range material, and is subjected to a hydrofinishing step.
 12. The process of claim 11 wherein the product of the catalytic dewaxing process is a lube base stock.
 13. The process of claim 12 wherein the molecular sieve is selected from the group consisting of ZSM-23, ZSM-35, ZSM-48, ZSM-22, SSZ-32, zeolite beta, mordenite, rare earth ion exchanged ferrierite and mixtures thereof.
 14. The process of claim 13 wherein the molecular sieve is ZSM-48.
 15. The process of claim 14 wherein the metal dehydrogenation component comprises a Group VIII metal.
 16. The process of claim 15 wherein the Group VIII metal is a noble metal.
 17. The process of claim 15 wherein the metal dehydrogenation component is a noble metal and the molecular sieve is ZSM-48. 